108,782 research outputs found

    Employment and Wages in Community and Social Service Occupations

    Get PDF
    People who work in community and social service occupations are concerned with improving society and the lives of individuals. These workers perform a diverse array of duties that may include counseling individuals with substance abuse and behavioral problems, providing social assistance to improve the social and psychological functioning of families, and offering spiritual and moral guidance to members of a faith. This issue of BEYOND THE NUMBERS will give a broad overview of employment and wages in community and social service occupations

    Prospects for Detection of Synchrotron Emission from Secondary Electrons and Positrons in Starless Cores: Application to G0.216+0.016

    Get PDF
    We investigate the diffusion of cosmic rays into molecular cloud complexes. Using the cosmic-ray diffusion formalism of Protheroe, et al. (2008), we examine how cosmic rays diffuse into clouds exhibiting different density structures, including a smoothed step-function, as well as Gaussian and inverse-rr density distributions, which are well known to trace the structure of star-forming regions. These density distributions were modelled as an approximation to the Galactic centre cloud G0.216+0.016, a recently-discovered massive dust clump that exhibits limited signs of massive star formation and thus may be the best region in the Galaxy to observe synchrotron emission from secondary electrons and positrons. Examination of the resulting synchrotron emission, produced by the interaction of cosmic ray protons interacting with ambient molecular matter producing secondary electrons and positrons reveals that, due to projection effects, limb-brightened morphology results in all cases. However, we find that the Gaussian and inverse-rr density distributions show much broader flux density distributions than step-function distributions. Significantly, some of the compact (compared to the 2.2′′2.2'' resolution, 5.3 GHz JVLA observations) sources show non-thermal emission, which may potentially be explained by the density structure and the lack of diffusion of cosmic rays into the cloud. We find that we can match the 5.3 and 20 GHz flux densities of the non-thermal source JVLA~1 and 6 from Rodr\'{\i}guez & Zapata (2014) with a local cosmic ray flux density, a diffusion coefficient suppression factor of χ=0.1−0.01\chi=0.1-0.01 for a coefficient of 3×10273\times10^{27} cm2^2 s−1^{-1}, and a magnetic field strength of 470 μ\muG.Comment: 4 pages, 2 figures, accepted for publication in the Astrophysical Journal Letter

    Pulsar state switching, timing noise and free precession

    Full text link
    Recent radio pulsar observations have shown that a number of pulsars display interesting long term periodicities in their spin-down rates. At least some of these pulsars also undergo sharp changes in pulse profile. This has been convincingly attributed to the stars abruptly switching between two different magnetospheric states. The sharpness of these transitions has been taken as evidence against free precession as the mechanism behind the long term variations. We argue that such a conclusion is premature. By performing a simple best-fit analysis to the data, we show that the relationship between the observed spin and modulation periods is of approximately the correct form to be accounted for by the free precession of a population of neutron stars with strained crusts, the level of strain being similar in all of the stars, and consistent with the star retaining a memory of a former faster rotation rate. We also provide an argument as to why abrupt magnetospheric changes can occur in precessing stars, and how such changes would serve to magnify the effect of precession in the timing data, making the observation of the precession more likely in those stars where such switching occurs. We describe how future observations could further test the precession hypothesis advanced here.Comment: Additional reference inserted; to appear in MNRA

    An Overview of Employment and Wages in Science, Technology, Engineering and Math (STEM) Groups

    Get PDF
    STEM is an acronym often used to refer to occupations, as well as fields of study, in science, technology, engineering, and math. The definition of STEM can vary, depending on the group using it. To develop some standards, the Standard Occupation Classification Policy Committee, made up of representatives of several government agencies, developed options for defining STEM occupations, using the 2010 Standard Occupational Classification (SOC) system. The SOC Policy Committee developed two major domains that contain two subdomains each. The first major domain contains the core STEM occupations, and the second domain includes occupations that are dependent upon STEM knowledge. The domains, subdomains, and the five types of STEM occupations are all groupings based on the type of occupations and the duties associated with each particular type of occupation that should prove useful for workforce planning and development, human resource departments, and jobseekers. This Beyond the Numbers article describes the employment and wages for these STEM groups, using Occupational Employment Statistics (OES) data from the Bureau of Labor Statistics

    Parameter choices and ranges for continuous gravitational wave searches for steadily spinning neutron stars

    Full text link
    We consider the issue of selecting parameters and their associated ranges for carrying out searches for continuous gravitational waves from steadily rotating neutron stars. We consider three different cases (i) the "classic" case of a star spinning about a principal axis; (ii) a biaxial star, not spinning about a principal axis; (iii) a triaxial star spinning steady, but not about a principal axis (as described in Jones, MNRAS vol 402, 2503 (2010)). The first of these emits only at one frequency; the other two at a pair of harmonically related frequencies. We show that in all three cases, when written in terms of the original "source parameters", there exist a number of discrete degeneracies, with different parameter values giving rise to the same gravitational wave signal. We show how these can be removed by suitably restricting the source parameter ranges. In the case of the model as written down by Jones, there is also a continuous degeneracy. We show how to remove this through a suitable rewriting in terms of "waveform parameters", chosen so as to make the specialisations to the other stellar models particularly simple. We briefly consider the (non-trivial) relation between the assignment of prior probabilities on one set of parameters verses the other. The results of this paper will be of use when designing strategies for carrying out searches for such multi-harmonic gravitational wave signals, and when performing parameter estimation in the event of a detection.Comment: Updated to match version accepted by MNRAS: One new equation (equation 82)); typo (sign-error) corrected in equation (88); one more paragraph inserted into Summary and Discussion sectio

    Growth: With or Without Scale Effects?

    Get PDF
    December 15, 1998 -- Version 1.0 The property that ideas are nonrivalrous leads to a tight link between idea-based growth models and increasing returns to scale. In particular, changes in the size of an economy's population generally affect either the long-run growth rate or the long-run level of income in such models. This paper provides a partial review of the expanding literature on idea-based models and scale effects. It presents simple versions of various recent idea-based growth models and analyzes their implications for the relationship between scale and growth. Prepared for the AEA Meetings, January 3, 1999. Forthcoming in the AER Papers and Proceedings, May 1999.

    Why Have Health Expenditures as a Share fo GDP Risen So Much?

    Get PDF
    Aggregate health expenditures as a share of GDP have risen in the United States from about 5 percent in 1960 to nearly 14 percent in recent years. Why? This paper explores a simple explanation based on technological progress. Medical advances allow diseases to be cured today, at a cost, that could not be cured at any price in the past. When this technological progress is combined with a Medicare- like transfer program to pay the health expenses of the elderly, the model is able to reproduce the basic facts of recent U.S. experience, including the large increase in the health expenditure share, a rise in life expectancy, and an increase in the size of health-related transfer payments as a share of GDP.

    Three evolutionary paths for magnetar oscillations

    Full text link
    Quasi-periodic oscillations have been seen in the light curves following several magnetar giant flares. These oscillations are of great interest as they probably provide our first ever view of the normal modes of oscillation of neutron stars. The state-of-the-art lies in the study of the oscillations of elastic-magnetic stellar models, mainly with a view to relating the observed frequencies to the structure and composition of the star itself. We advance this programme by considering several new physical mechanisms that are likely to be important for magnetar oscillations. These relate to the superfluid/superconducting nature of the stellar interior, and the damping of the modes, both through internal dissipation mechanisms and the launching of waves into the magnetosphere. We make simple order-of-magnitude estimates to show that both the frequencies and the damping time of magnetar oscillations can evolve in time, identifying three distinct `pathways' that can be followed, depending upon the initial magnitude of the mode excitation. These results are interesting as they show that the information buried in magnetar QPOs may be even richer than previously thought, and motivate more careful examination of magnetar light curves, to search for signatures of the different types of evolution that we have identified.Comment: To appear in MNRAS. This version reflects changes made in response to referee's comments, mainly extra discussion in Section 2.
    • …
    corecore